Dicarboxylate esters of alcohol containing a quaternary carbon in the beta-position

ABSTRACT

Hydraulic fluids, heat transfer fluids or synthetic lubricants comprise a diester of a saturated aliphatic, saturated cycloaliphatic or aromatic dicarboxylic acid having up to eleven carbon atoms in the molecule and one or two monohydric primary alcohols, which alcohols are free from aliphatic unsaturation, have from five to sixteen carbon atoms and have a quaternary carbon atom in the betaposition, together with a silicate, a hexaalkoxy disiloxane, a silicone, a phosphate ester or a mineral oil base.  The diesters may comprise a major or a minor proportion of the mixture.ALSO:The invention comprises a diester of a saturated aliphatic, saturated cycloaliphatic or aromatic dicarboxylic acid having up to eleven carbon atoms in the molecule and one or two monohydric primary alcohols, which alcohols are free from aliphatic unsaturation, have from five to sixteen carbon atoms and have a quaternary carbon atom in the beta-position.  A preferred class of alcohols are those of the formula R1.C(R2)(R3).CH2.OH, in which R1, R2 and R3 are all alkyl groups, preferably n-alkyl groups. Another preferred group of alcohols is that in which the beta-carbon atom is part of a cycloalkyl group containing five or six carbon atoms. The compounds may be prepared by the usual esterification procedures, e.g. by heating the acid or acid halide with a slight excess of the alcohol using sulphuric acid as an esterification catalyst, and removing water azeotropically by distilling in the presence of toluene.  An alternative procedure involves ester interchange using an ester of the dicarboxylic acid with an alcohol of low molecular weight, such as methanol, in the presence of a catalyst.  The esters find use in hydraulic fluids, heat transfer fluids or synthetic lubricants (see Group III). Detailed examples of the preparation of diesters are given.  One example also describes the preparation of 2,2,4-trimethyl-1-pentanol by reacting 2,2,4-trimethyl-1,3-pentanediol with acetyl chloride to form 2,2,4-trimethyl-1,3-diacetoxypentane, selectively pyrolysing the latter to form 2,2,4-trimethyl-3-penten-1-yl-acetate, and then reducing the acetate using hydrogen with a palladium on carbon catalyst to form the 2,2,4-trimethyl-1-pentanol.

Edward Blake and William c. Hammann, Dayton, Ohio, assignors to Monsanto Chemical Company, St. Louis, Mo., a corporation of Delaware No Drawing. Application October 6, 1955 Serial No. 539,007

1': Claims. (Cl. 260-468 This invention relates to a particular class of novel diesters having outstanding viscosity and thermal stability characteristics which make the esters especially suitable for use as functional fiuids-ie, hydraulic fluids, heat transfer fluids, synthetic lubricants and the like.

Other diesters have previously been utilized as func tional fluids, but these prior fiuids are not sufficiently stable for some of the modern applications involving high temperature operating conditions. For example, synthetic lubritmnts for jet engines, hydraulic fluids for supersonic aircraft, coolants for electronic equipment, etc. are often required to withstand extended periods of operation at temperatures as high as 600 or 700 F. At these temperatures the prior art diester functional fluids completely decompose in a relatively short time, whereas the diesters of the present invention are quite stable.

, The novel compounds are diesters of certain dibasic acids which have been esterified by monohydric alcohols having only quaternary carbon atoms in the beta-position of said alcohol. The dibasic acids need not be esterified with only one alcohol, but may be esterified with two different alcohols provided both alcohols satisfy the criteria set forth below.

The acids from which the present diesters are formed are dicarboxylic acids which contain no more than 11 carbon atoms therein, and which preferably contain between about 6 and about carbon atoms, A pre ferred class of such dicarboxylic acids comprises the ali phatic (including cycloaliphatic) dicarboxylic acids. A further preferred class of acids comprises the saturated aliphatic dicarboxylic acids. Examples of suitable acids for formation of the present diesters are sebacic acid, adipic acid, glutaric acid, methylglutaric acid, pimelic acid, azelaic acid, iso sebacic acid, u-ethylsuberic acid, a,a'-diethyladipic acid, hexahydrophthalic acid, hexahydroisophthalic acid, hexahydrotcrephthalic acid, etc.

The critical criterion for the alcohols with which the foregoing dibasic acids are esterified is that such alco hols must have only quaternary carbon atoms in the beta positions thereof-Le, the carbon atom adjacent to the -CH OH carbinol group must be attached to four other adjacent carbon atoms. A further criterion of such alco hols is that they contain from 5 to 16, inclusive, carbon atoms, and preferably between 7 and 12, inclusive, car bon atoms. Primary alcohols are generally preferred over secondary and/or tertiary alcohols. One particularly preferred class of alcohols comprises compounds having the formula,

1 HOCH'!( IRz wherein the substituents R R and R; on the hetacarbon atom are all alkyl groups, and preferably all nalkyl groups. Another particularly preferred class of alcohols is made up of those compounds in which the beta-carbon atom is a member of a 5- or Gmcmber saturated aliphatic ring. Examples of suitable alcohols are 2,2,4trimethylpentyl alcohol, l-methylcyclohexylmethyl alcohol, 3 cyclopentyl-2,2-dimethyl-l-propanol, 2,2,6,6- tetramethylcyclohexanol, 2,2,5,itetramethylcyclopentanol, 2,2-dimethyi-l-butanol, 2,2-dimethyl-l-hexanol, 2,2- dimethyll-octanol, etc.

The present compounds can be prepared by usual esterification procedurese.g., by heating the acid in aslight excess of the alcohol with sulfuric acid as a cata= lyst, and then azeotroping off the water with toluene. The resulting crude products can be purified by diluting with a solvent, washing free of acid, drying over anhydrous sodium sulfate and vacuum distilling. The following examples are presented as illutrative of this general preparation as applied to particular compounds of the present invention.

EXAMPLE 1 Preparation of bis(2,2,4-Irimethylpentyl) sebacate To a mixture of 70 grams of 2,2,4 tn'methyl-1-pentanol and 50.5 grams of sebacic acid, there was added 0.5 cc. of sulfuric acid and sutficient toluene to azeotrope off the water and hold the reflux temperature below 130 C. The water which was removed (9 cc.) was collected in a Dean and Stark trap. Additional benzene was added and the ester was washed free of acid, dryed over anhydrous sodium sulfate and distilled through an 8-inch heated Vigreux column. The product was collected in 92 percent yield (106.5 grams) of bis(2,2,4-trimethyl-1- pentyl) sebacate: boiling 207209 C./0.6 mm.; n 1.4471. Analysis.-Calculated (as C H OQ: C, 73.3; H, 11.8. Found: C, 73.27; H, 11.76.

EXAMPLE 2 Preparation of 2,2,44rimeIhyI-I-pentanol This compound was prepared from 2,2,4-trimethyl-L3- pentanediol by converting the diol to 2,2,4-trimethyl-l,3- diacetoxypentane, selectively pyrolyzing the diacetoxypentane to form 2,2,4-trimethyl-3-penten-lyl acetate, and then reducing the acetate to the desired 2,2,4-trimethyll pentanol.

The 2,2,4-trimethyl-1,3-diacetoxypentane was prepared by adding (dropwise) 942 grams of acetyl chloride to a vigorously stirred solution of 876 grams of 2,2,4-trimethyl- 1,3-pentanediol in 1600 cc. of benzene and 1050 grams of pyridine. The mixture was held below 50 C. during the acetyl chloride addition, then heated at C. for 1 hours. The reaction mixture was cooled, diluted with 400 cc. of benzene, washed free of pyridine hydro chloride, dried over anhydrous sodium sulfate and topped under water pump vacuum. Fractionation through an 8-inch Vigreux column gave a 90 percent yield (1380 grams) of the diacetate: boiling 1l5-116 C./l0 mm.; 11,, 1,4308.

One-thousand two hundred and eighty-one grams of the above 2,2,4 trimethyll,3-diacetoxypentane was dropped through a vertical pyrolysis tube at 494-5l7 C. over a period of 17 hours, and the effluent was collected under a water-cooled reflux condenser. The pyrolysis tube was a pyrex glass tube approximately 25 mm. in diameter and 48 inches long packed with size 3 solid glass beads over a length of 32 inches; it was insulated and electrically heated over approximately 38 inches, with separate heating elements for the top and bottom halves regulated by two powcrstats. The temperature was measured by two thermocouples located at distances approximately 8 and 24 inches in the bead bed. During the pyrolysis nitrogen was passed through the tube at a rate of 200 cc. per tninute.

The pyrolysis product was fractionated through a 90 x 2.5 cm. column packed with 6 mm. glass helices. By washing the forerun to remove acetic acid and redistilling the residue, there was obtained an 83.8 percent yield (644.2 grams) of clear colorless liquid 2,2,4 di methyl-B-penten-l-yl acetate: boiling 74.5-75.5 C./l2 mm; r1 1.4357. Analysis.-Calculated (as C H O c, 70.5; H, 10.6. Found: c, 70.0; H, 10.46.

The foregoing 2,2,4-trimethyl-3-penten-l-yl acetate was reduced at room temperature in a Parr hydrogenation apparatus using approximately 4 percent catalyst (5 percent palladium on carbon black) and 30 p.s.i.g. of hy drogen. The saturated reduction product was filtered to remove the catalyst, and the filtrate (472 g.) was hydrolyzed by refluxing for 5 hours in a solution of 1200 cc. of absolute ethanol and 100 cc. of water containing 111 grams of sodium hydroxide. The alcohol was removed by distillation, 200 cc. of water was added and the top layer was separated and washed free of caustic with saturated salt solution. The product was then dried over anhydrous sodium sulfate and vacuum distilled through a 30-inch Vigreux column to yield 346 grams (96 percent) of 2,2,4-tn'methy1-l-pentanol: boiling 8283 C./30 mm.: 11, 1.4280.

7 EXAMPLE 3 Preparation of bis(1 -methylcycl0hexylmethyl sebacale A mixture of 108 grams of sebacic acid, 158 grams of 1-methy1cyelohexylmethanol, 1 gram of concentrated sulfuric acid and 50 cc. of toluene was heated at reflux under a Dean and Stark trap until 17.5 cc. of Water had been collected. The reaction mixture was cooled and dissolved in one liter of ether. The ether solution was washed with four 100 cc. portions of 5 percent sodium hydroxide solution and six 250 cc. portions of water and then dried over sodium sulfate. The solvent and drying agent were removed and the residue was fractionated under vacuum through a lO-inch column packed with 4 mm. glass helices. The product was obtained in 73 percent yield (166 grams) of colorless, oily bis(l-methylcyclohexylmethyl) sebacate: boiling 2l52l7 C./0.4 mm.; 1.4725. Analysis.Calculated (as C H O C, 73.89; H, 10.97. Found: C, 74.17; H, 11.28.

EXAMPLE 4 Preparation of bis(l-mel/zylcyclohexylmethyl) adipale EXAMPLE 5 Preparation of bi.r(Imethylcycl0hexylnzethyl) lzexahydroisophlhalate A mixture of 80 grams of 1'methylcyclohexylmethanol, 60 grams of dimethylhexahydroisophthalate and 0.25 grams of sodium was heated under a Dean and Stark trap for 1% hours at 165 C., after which time the temperature was raised to 210 C. for /2 hour. During this period 24 cc. of methanol distillate was collected in the trap. The reaction product was dissolved in ether, washed free of caustic, dried over sodium sulfate and twice distilled under vacuum through a lO-inch heated Vigreux column to give a yield of 72 grams of bis(1- methylcyclohexylmethyl) hexahydroisophthalate: boiling 217220 C./1.3l.4 mm.; 11 1.4865. Analysis. Calculated (as C H O C, 73.4; H, 10.19. Found: C, 73.83; H, 9.83.

The abovedescribed esters are particularly useful as functional fluids because of their outstanding properties 4 with respect to volatility, pour point, viscosity, hydrolytic stability and thermal stability. The particularly outstanding property of thermal stability is illustrated in the fol lowing example, showing a comparison of the dicsters of the present invention with dicsters which do not have quaternary carbon atoms in the beta-position of the alcohol moiety.

EXAMPLE 6 Percent Percent loss Compound loss in 210 vLsweight cosity Di(noety1) sebacato 62 Bis(2ethylhexyl) scbamte 64 Bis(2,2,441'lmethyl-Lpentyl) sebneate. t. 8. 5 l0. 7 Bis(l-rnethyelyelohexyhnethyl) sebaeate. 1.3 12. 9 Bis(1-n1ethyleyclohexyl-inethyl) hexahydr ph thalate l. 2 9. 6 Bis(l-rnethylcyeloberyl-methyl) adipate 5. 5 7. 5

From the foregoing table it can be seen that the diesters of the present invention are as much as times more stable (as measured by percent loss in weight) than the comparable prior art diesters. The change in viscosity of the prior art diesters could not be measured because of a large amount of solid deposits resulting from substantially complete decomposition of the diesters.

When utilized as functional fluids the present diesters, or mixture thereof, will generally comprise a major or predominant portion of the composition. There may, however, be minor proportions of V.I. irnprovers, dyes, antioxidants, hydrolysis inhibitors, snuffer additives, antiwear additives, diluents and similar commonly used addilives incorporated herein in order to impart special properties to the fluids for particular specialty applications.

The present dicsters can also be utilized in combination with one or more other functional fluid bases, such as silicates (e.g., tetra(2-ethylhexyl)orthosilicate, tetra(2- cthylbutyl)silicate, tetra(4 methyl 2 pentyl)silicate), hexaalkoxy disiloxancs (e. g., hexa(2ethylhexyl)disiloxane, hexzi(Z'ethyIbutyl)disiloxane), silicones (e.g., phenylmethyl silicone, methyl silicones), phosphate esters (e.g., tricrcsyl phosphate, tri-Z-ethylhexyl) phosphate, mineral oil functional fluid bases, and similar mixtures, wherein the present dicsters comprise either a major or minor proportion of the mixture.

\Ve claim:

1. A diester of (a) a saturated aliphatic dicarboxylic acid containing not more than 11 carbon atoms and (b) a saturated aliphatic monohydric primary alcohol containing from 7 to 12 carbon atoms, the betacarbon atom being a quaternary carbon atom and a part of a ring selected from the group consisting of 5- and 6-membcred alicyclic rings.

2. The diester of claim 1, wherein the alcohol is lmethylcyclohexylmethyl alcohol.

3. The diester of claim 2, bis( l-methylcyclohexyl methyl) sebacate.

4. The diestcr of claim 2, bis(l-methylcyc1ohexylmethyl) adipate.

5. The diester of claim 2, bis(l-methylcyclohexyl methyl) hexahydroisophthalate.

6. A thermally stable functional fluid suitable for use at high temperatures and essentially containing, as substantially the sole dicarboxylate esters therein, dicsters at high temperatures and essentially contaiuing,;as substantially the sole dicarboxylate esters therein, diesters of (a) saturated aliphatic dimrboxylic acids containing not more than 11 carbon atoms and (b) aliphatic monohydric alcohols containing from 7 to 12 carbon atoms and having the formula wherein R R and R are satilrated galiphatic hydrocarbon radicals; and said diesters of (a) and (b) are present in an amount of at least 50 weight percent of the thermally stable functional fluid composition.

8. The functional fluid of claim 7, wherein the aliphatic nionohydric alcohol is 2,2,4-trimethylpentyl alcohol.

9. The functional fluid of claim 7, wherein the diester is bis(2,2,4-trimethylpentyl) sebacate.

10. A thermally stable functional fluid suitable for use at high temperatures and essentially containing, as substantially the sole dicarboxylate esters therein, diesters of (a) saturated aliphatic dicarboxylic acids containing not more than 11 carbon atoms and (b) aliphatic monohydric alcohols containing from 7 to 12 carbon atoms and having the formula B1 Ho-oHrb-n,

wherein R R and R are n-alkyl radicals; and said diesters of (a) and (b) are present in an amount of at least weight percent of the thermally stable funciional fluid composition.

ll. A thermally stable functional fluid suitable for use at high temperatures and essentially containing, as substantially the sole dicarboxylate esters therein, diesters of (a) saturated aliphatic dicarboxylic acids containing not more than 11 carbon atoms and (b) saturated aliphatic monohydric primary alcohols containing from 7 to 12 carbon atoms, the fl-carbon atom being a quaternary carbon atom and a part of a ring selected from the group consisting of 5- and G-membered alicyclic rings; and said diesters of (a) and (b) are present in an amount of at least 50 weight percent of the thermally stable functional fluid composition. y

12. The functional fluid of claim 11, wherein the alcohol is l-methylcyclohexylmethyl alcohol.

13. The functional fluid of claim 6, wherein the dica-rboxylic acid is hexahydrophthalic acid.

References Cited in the file of this patent UNITED STATES PATENTS 1,646,128 VanSchaack Oct. 18, 1927 1,708,404 Zimmerli Apr. 9, 1929 2,368,765 Lawrence Feb. 6, 1945 2,593,428 Fischer et al. Apr. 22, 1952 2,699,434 Turck Jan. 11, 1955 2,792,417 Dean May 14, 1957 FOREIGN PATENTS 1,041,934 France June 3, 1953 

1. A DIESTER OF (A) A SATURATED ALIPHATIC DICARBOXYLIC ACID CONTAINING NOT MORE THAN 11 CARBON ATOMS AND (B) A SATURATED ALIPHATIC MONOHYDRIC PRIMARY ALCOHOL CONTAINING FROM 7 TO 12 CARBON ATOMS, THE BETA-CARBON ATOMS BEING A QUATERNARY CARBON ATOM AND A PART OF A RING SELECTED FROM THE GROUP CONSISTING OF 5- AND L-MEMBERED ALICYCLIC RINGS.
 10. A THERMALLY STABLE FUNCTIONAL FLUID SUITABLE FOR USE AT HIGH TEMPRATURES AND ESSENTIALLY CONTAINING, AS SUBSTANTIALLY THE SOLE DICARBOXYLATE ESTERS THEREIN, DIESTERS OF (A) SATURATED ALIPHATIC DICARBOXYLIC ACIDS CONTAINING NOT MORE THAN 11 CARBON ATOMS AND (B) ALIPHATIC MONOHYDRIC ALCOHOLS CONTAINING FROM 7 TO 12 CARBON ATOMS AND HAVING THE FORMULA 